Identification bits are useful in an ink-jet pen, e.g. a thermal ink-jet pen, to identify the pen model, ink color, ink fill and other parameters. Electrical interconnects are used to read this identification from the standard pen electrical interface. The number of interconnections is limited by cost and available space on the printhead die.
The typical technique for encoding information is illustrated in FIG. 1, and uses a single low resistance connection or link 12A-12N for each printhead address bit A(O), A(1). . . A(N), connecting each address select transistor 10A, 10B . . . 10N to a common "sense" line 14 through a resistance 16A, 16B . . . 16N. Information is stored by connecting or not connecting each of these links 12A-12N. Since there are only two possible states for this link, the number of possible states is 2.sup.N possible states. The information is read by a resistance measurement on the sense line.
It would be an advantage to be able to store and access more information per interconnect than is provided by existing techniques.